Composites and methods for treating bone

ABSTRACT

A system and method for treating bone abnormalities including vertebral compression fractures and the like. In one vertebroplasty method, a fill material is injected under high pressures into cancellous bone wherein the fill material includes a flowable bone cement component and an elastomeric polymer component that is carried therein. The elastomer component can further carry microscale or mesoscale reticulated elements. Under suitable injection pressures, the elastomeric component ultimately migrates within the flowable material to alter the apparent viscosity across the plume of fill material to accomplish multiple functions. For example, the differential in apparent viscosity across the fill material creates a broad load-distributing layer within cancellous bone for applying retraction forces to cortical bone endplates. The differential in apparent viscosity also transitions into a flow impermeable layer at the interface of cancellous bone and the flowable material to prevent extravasion of the flowable bone cement component.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of Provisional U.S. Patent ApplicationSer. No. 60/578,182 filed Jun. 9, 2004 (Docket No. S-7700-030) titledScaffold Composites and Methods for Treating Abnormalities in Bone, theentire contents of which are hereby incorporated by reference in theirentirety and should be considered a part of this specification.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to bone implant materials and methods and moreparticularly to composite materials including an elastomer component fortreating abnormalities in bones such as compression fractures ofvertebra, necrosis of femurs, joint implants and the like. An exemplarymethod includes introducing a flowable composite material into theinterior of a bone wherein increasing pressures result in the elastomercomponent causing a differential apparent viscosity within selectedregions across the flowable material to thereby allow controlledapplication of forces to the bone for reducing a fracture.

2. Description of the Related Art

Osteoporotic fractures are prevalent in the elderly, with an annualestimate of 1.5 million fractures in the United States alone. Theseinclude 750,000 vertebral compression fractures (VCFs) and 250,000 hipfractures. The annual cost of osteoporotic fractures in the UnitedStates has been estimated at $13.8 billion. The prevalence of VCFs inwomen age 50 and older has been estimated at 26%. The prevalenceincreases with age, reaching 40% among 80-year-old women. Medicaladvances aimed at slowing or arresting bone loss from aging have notprovided solutions to this problem. Further, the affected populationwill grow steadily as life expectancy increases. Osteoporosis affectsthe entire skeleton but most commonly causes fractures in the spine andhip. Spinal or vertebral fractures also have serious consequences, withpatients suffering from loss of height, deformity and persistent painwhich can significantly impair mobility and quality of life. Fracturepain usually lasts 4 to 6 weeks, with intense pain at the fracture site.Chronic pain often occurs when one level is greatly collapsed ormultiple levels are collapsed.

Postmenopausal women are predisposed to fractures, such as in thevertebrae, due to a decrease in bone mineral density that accompaniespostmenopausal osteoporosis. Osteoporosis is a pathologic state thatliterally means “porous bones”. Skeletal bones are made up of a thickcortical shell and a strong inner meshwork, or cancellous bone, ofcollagen, calcium salts and other minerals. Cancellous bone is similarto a honeycomb, with blood vessels and bone marrow in the spaces.Osteoporosis describes a condition of decreased bone mass that leads tofragile bones which are at an increased risk for fractures. In anosteoporotic bone, the sponge-like cancellous bone has pores or voidsthat increase in dimension, making the bone very fragile. In young,healthy bone tissue, bone breakdown occurs continually as the result ofosteoclast activity, but the breakdown is balanced by new bone formationby osteoblasts. In an elderly patient, bone resorption can surpass boneformation thus resulting in deterioration of bone density. Osteoporosisoccurs largely without symptoms until a fracture occurs.

Vertebroplasty and kyphoplasty are recently developed techniques fortreating vertebral compression fractures. Percutaneous vertebroplastywas first reported by a French group in 1987 for the treatment ofpainful hemangiomas. In the 1990's, percutaneous vertebroplasty wasextended to indications including osteoporotic vertebral compressionfractures, traumatic compression fractures, and painful vertebralmetastasis. In one percutaneous vertebroplasty technique, bone cementsuch as PMMA (polymethylmethacrylate) is percutaneously injected into afractured vertebral body via a trocar and cannula system. The targetedvertebrae are identified under fluoroscopy. A needle is introduced intothe vertebral body under fluoroscopic control to allow directvisualization. A transpedicular (through the pedicle of the vertebrae)approach is typically bilateral but can be done unilaterally. Thebilateral transpedicular approach is typically used because inadequatePMMA infill is achieved with a unilateral approach.

In a bilateral approach, approximately 1 to 4 ml of PMMA are injected oneach side of the vertebra. Since the PMMA needs to be forced intocancellous bone, the technique requires high pressures and fairly lowviscosity cement. Since the cortical bone of the targeted vertebra mayhave a recent fracture, there is the potential of PMMA leakage. The PMMAcement contains radiopaque materials so that when injected under livefluoroscopy, cement localization and leakage can be observed. Thevisualization of PMMA injection and extravasion are critical to thetechnique and the physician terminates PMMA injection when leakage isevident. The cement is injected using small syringe-like injectors toallow the physician to manually control the injection pressures.

Kyphoplasty is a modification of percutaneous vertebroplasty.Kyphoplasty involves a preliminary step that comprises the percutaneousplacement of an inflatable balloon tamp in the vertebral body. Inflationof the balloon creates a cavity in the bone prior to cement injection.Further, the proponents of percutaneous kyphoplasty have suggested thathigh pressure balloon-tamp inflation can at least partially restorevertebral body height. In kyphoplasty, it has been proposed that PMMAcan be injected at lower pressures into the collapsed vertebra since acavity exists to receive the cement—which is not the case inconventional vertebroplasty.

The principal indications for any form of vertebroplasty areosteoporotic vertebral collapse with debilitating pain. Radiography andcomputed tomography must be performed in the days preceding treatment todetermine the extent of vertebral collapse, the presence of epidural orforaminal stenosis caused by bone fragment retropulsion, the presence ofcortical destruction or fracture and the visibility and degree ofinvolvement of the pedicles. Leakage of PMMA during vertebroplasty canresult in very serious complications including compression of adjacentstructures that necessitate emergency decompressive surgery.

Leakage or extravasion of PMMA is a critical issue and can be dividedinto paravertebral leakage, venous infiltration, epidural leakage andintradiscal leakage. The exothermic reaction of PMMA carries potentialcatastrophic consequences if thermal damage were to extend to the duralsac, cord, and nerve roots. Surgical evacuation of leaked cement in thespinal canal has been reported. It has been found that leakage of PMMAis related to various clinical factors such as the vertebral compressionpattern, and the extent of the cortical fracture, bone mineral density,the interval from injury to operation, the amount of PMMA injected andthe location of the injector tip. In one recent study, close to 50% ofvertebroplasty cases resulted in leakage of PMMA from the vertebralbodies. See Hyun-Woo Do et al, “The Analysis of PolymethylmethacrylateLeakage after Vertebroplasty for Vertebral Body Compression Fractures”,Jour. of Korean Neurosurg. Soc. Vol. 35, No. 5 (May 2004) pp. 478-82,(http://www.jkns.or.kr/htm/abstract.asp?no=0042004086).

Another recent study was directed to the incidence of new VCFs adjacentto the vertebral bodies that were initially treated. Vertebroplastypatients often return with new pain caused by a new vertebral bodyfracture. Leakage of cement into an adjacent disc space duringvertebroplasty increases the risk of a new fracture of adjacentvertebral bodies. See Am. J. Neuroradiol. 2004 February; 25(2):175-80.The study found that 58% of vertebral bodies adjacent to a disc withcement leakage fractured during the follow-up period compared with 12%of vertebral bodies adjacent to a disc without cement leakage.

Another life-threatening complication of vertebroplasty is pulmonaryembolism. See Bernhard, J. et al., “Asymptomatic diffuse pulmonaryembolism caused by acrylic cement: an unusual complication ofpercutaneous vertebroplasty”, Ann. Rheum. Dis. 2003; 62:85-86. Thevapors from PMMA preparation and injection are also cause for concern.See Kirby, B., et al., “Acute bronchospasm due to exposure topolymethylmethacrylate vapors during percutaneous vertebroplasty”, Am.J. Roentgenol. 2003; 180:543-544.

Another disadvantage of PMMA is its inability to undergo remodeling—andthe inability to use the PMMA to deliver osteoinductive agents, growthfactors, chemotherapeutic agents and the like. Yet another disadvantageof PMMA is the need to add radiopaque agents which lower its viscositywith unclear consequences on its long-term endurance.

In both higher pressure cement injection (vertebroplasty) andballoon-tamped cementing procedures (kyphoplasty), the methods do notprovide for well controlled augmentation of vertebral body height. Thedirect injection of bone cement simply follows the path of leastresistance within the fractured bone. The expansion of a balloon alsoapplies compacting forces along lines of least resistance in thecollapsed cancellous bone. Thus, the reduction of a vertebralcompression fracture is not optimized or controlled in high pressureballoons as forces of balloon expansion occur in multiple directions.

In a kyphoplasty procedure, the physician often uses very high pressures(e.g., up to 200 or 300 psi) to inflate the balloon which first crushesand compacts cancellous bone. Expansion of the balloon under highpressures close to cortical bone can fracture the cortical bone, orcause regional damage to the cortical bone that can result in corticalbone necrosis. Such cortical bone damage is highly undesirable andresults in weakened cortical endplates.

Kyphoplasty also does not provide a distraction mechanism capable of100% vertebral height restoration. Further, the kyphoplasty balloonsunder very high pressure typically apply forces to vertebral endplateswithin a central region of the cortical bone that may be weak, ratherthan distributing forces over the endplate.

There is a general need to provide systems and methods for use intreatment of vertebral compression fractures that provide a greaterdegree of control over introduction of bone support material, and thatprovide better outcomes. Embodiments of the present invention meet oneor more of the above needs, or other needs, and provide several otheradvantages in a novel and non-obvious manner.

SUMMARY OF THE INVENTION

The invention provides systems and method of treating bone abnormalitiesincluding vertebral compression fractures, bone tumors and cysts,avascular necrosis of the femoral head and the like. In one embodiment,the invention comprises a bone infill system or implant system with afill material that includes a flowable component and an elastomericpolymer component that is deformable in-situ (FIG. 1A). In oneembodiment, the elastomer component comprises a matrix of base elastomerand a filler of microscale or mesoscale reticulated elements (FIG. 1B).The elastomeric component corresponding to the invention performsmultiple functions, for example, (i) forming a load-distributingstructure between a bone fill material or structure and the elastomercomponent; (ii) mechanically creating a seal at the interface ofcancellous bone and bone fill material or structure to preventextravasion of a flowable material, (iii) creating a substantiallyporous layer around the surface of non-porous bone fill material orstructures and/or (vi) creating an insulative layer around the surfaceof an exothermic bone fill material. The elastomer component can be usedin bone support treatments or in treatments to move apart cortical bonesurfaces as in treating vertebral compression fractures.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following detailed description, similar reference numerals areused to depict like elements in the various figures.

FIG. 1A is a greatly enlarged sectional view of a flowable compositebone infill material such as PMMA with a volume of elastomeric elementsor particles carried therein.

FIG. 1B is a greatly enlarged sectional view of an elastomeric elementof FIG. 1A with reticulated elements dispersed within the elastomer.

FIG. 2A is a schematic view of a spine segment with a vertebra having acompression fracture showing a method of the invention wherein a volumeof the flowable media of FIG. 1A is injected under pressure intocancellous bone in a targeted treatment site.

FIG. 2B is a schematic view of the spine segment of FIG. 2A showing thepressurized injection of additional flowable wherein the apparentviscosity of the media is altered at surface regions of the plume byoutward migration of the elastomeric element to thereby createflow-impermeable surface regions.

FIGS. 3A-3B are schematic sectional views of a monolith implantstructure fabricated of the composite elastomeric material of FIG. 1B;with FIG. 3A illustrating the implant structure introduced into a borein a bone.

FIG. 3B illustrate the elastomeric material of FIG. 3A being inserted inthe bore in the bone.

FIG. 3C illustrates an interference fit bone screw driven into theelastomeric material of FIGS. 3A-3B which distributes loads about thebore in cancellous bone.

FIG. 4 is a sectional cut-away view of one an implant segment withmultiple layers having different moduli.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1A illustrates a cross-sectional view of fill material 4 thatcomprises flowable component 5 with elastomeric polymer component 6dispersed therein. The flowable component or material 5 is an in-situhardenable bone cement (e.g., PMMA) that is intermixed with elastomericcomponent 6 that comprises a plurality of small elastomeric elements,such as silicone particles or elements of another biocompatible polymer.The flowable material 5 and elastomeric elements 6 can be intermixedprior to introduction into bone or contemporaneous with introductioninto bone from separate channels in an introducer. The elastomericelements 6 are typically dimensioned to be small enough to allow theirpassage within the openings of cancellous bone in a targeted treatmentsite. In one embodiment as depicted in FIG. 1B, the elastomeric elements6 themselves comprise a composite of base elastomer 10A and reticulated,open-cell scaffold structures indicated at 10B. Such reticulatedopen-cell structures can allow for later bone ingrowth into the surfaceof the volume of fill material. The term “reticulated” as used hereindescribes open-cell structures 10B and means having the appearance of,or functioning as, a wire-like network or a substantially rigid net-likestructure. The terms reticulated and trabecular are used interchangeablyherein to describe structures having ligaments that bound open cells orclosed cells in the interior of the structure.

FIG. 2A-2B illustrate a method corresponding to the invention for use inthe treatment of a vertebral compression fracture indicated at 13. InFIG. 2A, an initial volume of fill material 4 comprising a flowable bonecement component 5 and intermixed elastomeric elements 6 is injectedunder substantial pressure into cancellous bone 14 of the vertebra 15resulting in plume 18. The fill material 4 is introduced in a unilateralor bilateral transpedicular approach through cannula 19 as is well knownin the art of vertebroplasty. The fill material 4 propagates within theopenings in cancellous bone and may also follow pre-existing fracturelines in cancellous bone, for example as may exist following acompression fracture. FIG. 2B illustrates the same step of injectingfill material 4 but after a greater volume of material has beenintroduced resulting in plume 18 of fill material being larger andengaging the cortical bone endplates. In the high pressure injection ofa such a composite fill material, the elastomeric elements 6 migratetoward surface region 20 of plume 18 and create a differential in theapparent viscosity of the flowable material across the volume or plume.The term “apparent viscosity” is used herein to describe the flowcharacteristics of the combination of flowable component 5 andintermixed elastomeric elements 6. As the injection pressures and theresistance to inflows of fill material increase, the accumulation ofelastomeric elements 6 about surface region 20 also increases. Theelastomeric elements 6 can additionally deform and ultimately thepressures cause elastomeric elements 6 to form in-situ a substantiallyflow-impermeable surface region 20. As the surface region becomessubstantially impermeable to flows or extravasion therethrough offlowable component 5, continued injection of fill material willelastically expand the surface regions and apply expansion forces to thebone. In a vertebral body as in FIG. 2B, the expansion pressures canexpand cancellous bone 14 in which the flowable material 4 has flowedand apply retraction forces to the cortical bone endplates to at leastpartly reduce a vertebral fracture.

In general, an exemplary method corresponding to the invention fortreating mammalian bone comprises the following: (a) flowing an initialvolume of flowable media into the interior of a bone wherein the mediaincludes a volume of elastomeric elements, and (b) flowing underpressure increasing volumes of the flowable media wherein injectionpressures causes a differential apparent viscosity within selectedregions across the flowable media. The method further includes causingsurface regions 20 of the plume 18 of flowable media to be substantiallyimpermeable to flows therethrough (FIG. 2B). The method includesallowing an in-situ polymerizable component of the flowable media toharden to thereby support expanded cancellous bone and to maintainretracted cortical bone in an altered position.

In another embodiment, the fill material 4 described above includes anelastomer filler composite 6 that carries microscale or mesoscalereticulated elements 10B (FIG. 1B). As the elastomer elements 6aggregate about surface region 20 of the plume 18, the reticulatedmaterial is proximate to bone and can thus allow for subsequent boneingrowth. In addition, elastomer elements 6 and surface region 20 createan insulative layer that prevents or moderates heating of the boneexternal to surface region 20 from an exothermic reaction of a typicalbone cement used as flowable component 5 that is interior of surfaceregion 20.

In any embodiment, elastomer composite elements 6 can carryradiosensitive and magnetic-sensitive fillers for cooperating with an RFsource or an inductive heating source for elevating the polymer to atargeted temperature. Alternatively, the polymeric composition can besubstantially transparent or substantially translucent and carrychromophores for cooperating with a light source introduced with thematerial for heating to material to a selected temperature forincreasing the modulus of the material. Thus, such methods of heatingsurface regions 20 (FIG. 2B) in which the elastomer composite elements 6have aggregated will cause accelerated heating of adjacent interiorregions of flowable component 5. This system can be used to selectivelypolymerize regions of flowable media 5 adjacent the surface region 20.By this means, the peripheral portions of plume 18 interior of, andwithin, the aggregated elastomeric elements, can be formed into aflow-impermeable layer.

The reticulated structures 10B as in FIG. 1B define a mean cross sectionwhich can be expressed in microns. In preferred embodiments, the cellsare bounded by polyhedral faces, typically pentagonal or hexagonal, thatare formed with five or six ligaments 15. The cell dimension is selectedfor enhancing tissue ingrowth, and mean cell cross-sections can rangebetween 10 microns and 200 microns; and more preferably ranges between20 microns and 100 microns. Such reticulated materials and structuresare available from ERG Materials and Aerospace Corp., 900 StanfordAvenue, Oakland Calif. 94608 and Porvair Advanced Materials, Inc., 700Shepherd Street, Hendersonville N.C. 28792, and are more fully describedin co-pending U.S. patent application Ser. No. 11/______, filed Jun. 7,2005 (Docket No. S-7700-020A) titled Implants and Methods for TreatingBone, the contents of which are incorporated herein by this reference intheir entirety and should be considered a part of this specification.

Referring back to FIGS. 1A and 1B, the elastomeric composition comprisesany biocompatible polymer having an elastic modulus ranging betweenabout 10 MPa and 1 KPa. The polymer can be a foam, or a shape memorypolymer (SMP) that releases stored energy after heating and moving froma compacted temporary shape to an expanded memory shape. A descriptionof suitable shape memory polymers is described in U.S. patentapplication Ser. No. 10/837, 858 titled Orthopedic Implants, Methods ofUse and Methods of Fabrication filed May 3, 2004, the contents of whichare incorporated herein by this reference in their entirety and shouldbe considered a part of this specification. In a preferred embodiment,the elastomer elements 5 are at least one of bioerodible, bioabsorbableor bioexcretable.

FIGS. 3A-3C illustrate an alternative embodiment of the inventionwherein the composite of an elastomer 10A and reticulated elements 10B(FIG. 1B) is formed into exemplary implant body 40A. In FIGS. 3A and 3B,implant 40A is fabricated by molding in a suitable dimension forintroduction into bore 25 in a bone, indicated as cancellous bone 26 anda cortical bone surface 28. FIG. 3C illustrates that implant 40A canhave an optional channel or opening 44 for receiving or guiding thepositioning of fill material 48 comprising a threaded implant. In FIG.3C, it can be seen that a threaded implant 48 can be screwed into theimplant wherein the elastomeric implant 40A and reticulated elements 10Bdispersed therein are compressed to form an interference fit between thebone and implant member 40A. Of particular interest, the insertion ofthe threaded implant 48 causes self-adjustment of the distribution,location and orientation of the reticulated elements 10B within theelastomer matrix, thus optimally self-distributing loads between theimplant 48 and the bone. In the prior art, a threaded implant wouldengage the bone highest engagement pressures generally about the apex ofthe threads. In the system as in FIG. 3C, the engagement forces would bedistributed about all surfaces of threaded implant 48—which alsopreferably has a surface region that is reticulated, roughened orporous.

FIG. 4 illustrates another exemplary implant 40B that is fabricated ofan elastomer composite. In this embodiment, the composite body has atleast two layers 50 a and 50 b that are polymer matrices that carryreticulated elements having different parameters (density, celldimensions etc.) to provide different elastic moduli. The scope of theinvention thus encompasses an implant structure 40B that has a gradientmodulus for transitioning from an interface with cortical bone 55 to theinterface with a rigid member 48 which is needed in various implants andreconstructions, such as in hip implants.

In another embodiment depicted in FIGS. 5A and 5B, the elastomericcomposite implant 60 can be configured with a plurality of compositeregions 62 a and 62 b that provide variations or gradients in materialproperties for enhancing implant fixation in bone 64. In FIG. 5B, it canbe seen that regions 62 a of the composite are deformable but more rigidthan the adjacent regions 62 b. Thus, the higher modulus regions will beforced outward more into the bone that other regions 62 b upon insertionof bone screw 68. The scope of the invention encompasses varying all theobvious properties of different regions of the composite to achieve thedesired regional variations or gradients, and include adjusting the: (i)density of ligaments of the reticulated elements dispersed in thematrix; (ii) the overall shape, dimensions and orientations of thereticulated elements; (iii) the pore size of the reticulated elements;(iv) the modulus, deformability and material of the reticulatedelements; (v) the percentage volume of reticulated elements in thematrix, (vi) the properties media carried in the pores of thereticulated elements, and (vii) the modulus and other properties of thepolymer base material 10A (FIG. 1B).

The above-described embodiments describe elastomer composites thatcooperate with fill materials to control properties of the interfacebetween fill material and bone. The scope of the invention extends toelastomer composites as in FIGS. 2A-2B, 3A-3C and 4 that are introducedinto bone wherein a base polymer can be elevated to a transitiontemperature so that the composite then adjusts its orientation. Uponcooling, the elastomer composite can then freeze in a particular form.In such embodiments, it is preferred that reticulated elements in thecomposite have varied shapes for non-slip engagement between suchelements to thereby increase the modulus of the material. In anexemplary embodiment, the polymeric composition has a transitiontemperature in the range of 40° C. to 120° C.; and preferably in therange of 40° C. to 80° C. The transition temperature is a glasstransition temperature or a melt temperature. Again, the polymericmatrix can carry radiosensitive or magnetic-sensitive fillers forcooperating with an RF source or an inductive heating source forelevating the polymer to a targeted temperature. Alternatively, thepolymeric composition can be substantially transparent or substantiallytranslucent and carry chromophores for cooperating with a light sourcefor heating to material to a selected temperature for elevating thecomposition to a transition temperature.

In any embodiment, the fill materials or implants can further carry aradiopaque or radiovisible composition if the material of thereticulated elements is not radiovisible.

In any embodiment, the fill materials or implants can carry anypharmacological agent or any of the following: antibiotics, corticalbone material, synthetic cortical replacement material, demineralizedbone material, autograft and allograft materials. The implant body alsocan include drugs and agents for inducing bone growth, such as bonemorphogenic protein (BMP). The implants can carry the pharmacologicalagents for immediate or timed release.

The above description of the invention intended to be illustrative andnot exhaustive. A number of variations and alternatives will be apparentto one having ordinary skills in the art. Such alternatives andvariations are intended to be included within the scope of the claims.Particular features that are presented in dependent claims can becombined and fall within the scope of the invention. The invention alsoencompasses embodiments as if dependent claims were alternativelywritten in a multiple dependent claim format with reference to otherindependent claims.

1-31. (canceled)
 32. A method of treating mammalian bone, comprisingintroducing a flowable media under pressure into cancellous bone, themedia including a volume of elastomeric elements wherein the elastomericelements cause differential apparent viscosity within regions of theflowable media.
 33. The method of claim 32 wherein the elastomericelements cause surface regions of the flowable media to havesubstantially higher apparent viscosity than interior regions thereof.34. The method of claim 32 wherein the elastomeric elements causesurface regions of the flowable media to be substantially less permeableto flows therethrough.
 35. The method of claim 32 wherein introducingthe flowable media applies expansion forces to the bone substantiallywithout extravasation.
 36. The method of claim 32 wherein introducingthe flowable media expands the cancellous bone.
 37. The method of claim32 wherein introducing the flowable media includes introducing ahardenable cement.
 38. The method of claim 37 including permitting thecement to harden thereby providing support to the cortical bone aboutthe cancellous bone.
 39. The method of claim 32 wherein introducing theflowable media reduces a fracture.
 40. The method of claim 32 whereinintroducing the flowable media moves cortical bone.
 41. The method ofclaim 32 wherein introducing the flowable media increases height of afractured vertebra.
 42. The method of claim 32 further including thestep of applying energy to the elastomeric elements to heat the flowablemedia.
 43. The method of claim 42 wherein applying energy is carried outby at least one of a radiofrequency energy source and a light energysource.
 44. A method of treating mammalian bone, comprising flowing avolume of flowable composite media into cancellous bone and transformingthe surface regions of the flowable composite media to a substantiallyflow impermeable form while introducing additional flowable media intothe interior of volume.
 45. The method of claim 44 wherein transformingthe surface regions to a substantially flow impermeable form includescausing the aggregation of elastomeric elements in said surface regions.46. The method of claim 44 wherein transforming the surface regions to asubstantially flow impermeable form includes causing the expansion ofshape memory polymer elements.
 47. The method of claim 44 whereintransforming the surface regions to a substantially flow impermeableform includes delivering energy to said surface regions from a remoteenergy source.
 48. The method of claim 44 wherein flowing the volume ofcomposite media expands cancellous bone.
 49. The method of claim 44wherein flowing the volume of composite media moves cortical bone.
 50. Amethod of treating mammalian bone, comprising: introducing a volume ofelastomeric elements into the interior of a bone; and introducing aflowable media within the volume of elastomeric elements, wherein theelastomeric elements aggregate in outward regions of a plume of theflowable media to cause said outward regions to be substantiallyflow-impermeable.